Doing a garage's legwork for them

My car has got a knackered gearbox. It has been in the garage for a week now. Having heard nothing, I give them a call to find out what is going on. They then tell me that they can not source a gearbox and that I have to. Which leaves me in a bit of a pickle because realistically I don't know anything about gearboxes and am now stuck getting phone calls off brakers yards with quotes and I have no idea of what I need to ask!

Am I being completely unreasonable in thinking that this should be the garage's job? Or am I being naive?

Most garages have their preferred and trusted sources for second hand/refurbished parts and would be reluctant to buy from an unknown source in case the items were faulty or modified in some way.

Very few customers would be prepared to accept a bill for the cost of a replacement gearbox that might not be fit for purpose therefore it makes sense for the garage to ask the customer to source the part and pay labour only. The liability issue over the suitability of the gearbox then lies between the customer and the supplier, leaving the garage clear.

All well and good but if they can't source through their preferred vendors then surely they should tell me in order to allow me to make a decision about whether to move the car to another garage who could find the part or not?

I need this car for work and had I known this earlier I could have sourced the part by now (with BIL helping). As it stands it looks like another weekend and possibly week without my car.

Its not a particularly rare car, it is just sods law that they can't find this specific gearbox in their usual supppliers.

I have already sourced several others and am waiting for my BIL to contact them and check them out (he lives five hours away but is a mechanic). But I only had to use one (fairly reputable) website to get these. Why couldnt the garage do the same?